1. Field of the Invention
The present invention relates generally to lighting applications, and more particularly to an organic light emitting device and a light source comprising a plurality of organic light emitting devices mounted on a common substrate.
2. Description of the Related Art
There are many examples of lighting devices which comprise inorganic light emitting diodes (LEDs) or organic light emitting devices (OLEDs). One example is a commercially available blue-emitting inorganic gallium nitride LED which is coated with yellow-emitting phosphor particles to produce white light. The LED is essentially a point source of light rather than an extended area source of light.
An example of an OLED is set forth in U.S. Pat. No. 5,294,870, which describes an organic electroluminescent multicolor display device comprising an organic electroluminescent source emitting blue light with green- and red-emitting fluorescent materials applied to different subpixel areas. This device emits different colors from the different subpixel areas by color shifting with the green- and red-emitting fluorescent materials.
Another example of an OLED is described in Junji Kido et al., xe2x80x9cMultilayer White Light-Emitting Organic Electroluminescent Devicexe2x80x9d, 267 Science 1332-1334 (1995). This device includes three emitter layers with different carrier transport properties, each emitting blue, green, or red light, which layers are used to generate white light. This OLED outputs white light over an area which is greater than that of an inorganic LED. However, its emitting area is still relatively small.
In some lighting applications, it is desirable to have extended area light sources. Although it is theoretically possible to increase the size of known OLED devices by using larger equipment, the process of coating thin, high quality organic layers over large areas may present many technical challenges. Issues that would typically need to be addressed in scaling up production to larger sizes include, for example, uniformity of coating thickness, pinholes, particulates, CTE mismatches during thermal excursions, organic material stability to processing chemicals, and adhesion to organic and inorganic interfaces. Moreover, a defect anywhere in a large panel may necessitate scrapping the entire panel. Large equipment is also more costly.
It would be desirable, therefore, to have a light source with a large emitting area and an effective method of making such a light source.
The invention relates to a light source comprising a mounting substrate, at least two organic light emitting devices mounted on the mounting substrate, each of the at least two organic light emitting devices comprising a first electrode which is light transmissive, an organic light emitting layer, a second electrode, a first device electrical contact extending from the first electrode to the mounting substrate, and a second device electrical contact extending from the second electrode to the mounting substrate.
The invention also relates to an organic light emitting device comprising a first electrode which is light transmissive, an organic light emitting layer positioned adjacent to the first electrode, the organic light emitting layer having an imaginary surface running therethrough defining a first side and a second side of the organic light emitting device, wherein the first electrode is on the first side of the organic light emitting device, a second electrode positioned adjacent to the organic light emitting layer on the second side of the organic light emitting device, a first device electrical contact extending from the first electrode to the second side of the organic light emitting device, and a second device electrical contact extending from the second electrode.
The invention also relates to a method of making a light source comprising the steps of providing a plurality of organic light emitting devices, each of the organic light emitting devices having first and second device electrical contacts which have respective first and second device contacting surfaces which occupy a common plane, the first and second device electrical contacts being electrically connected with first and second electrodes of the organic light emitting device, respectively, and mounting the plurality of organic light emitting devices on a mounting substrate such that the first and second device contacting surfaces make electrical contact with corresponding first and second mounting electrical contacts on the mounting substrate.